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Loss Per Share - Additional Information (Detail) - shares
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Earnings Per Share [Abstract]          
Options to purchase shares, restricted share awards, and contingently issuable shares excluded from diluted net loss per share computation 7,900,000 10,100,000 8,300,000 10,300,000  
Common stock outstanding 115,765,255   115,765,255   117,096,731